AB-INITIO STUDY OF THE STRUCTURES AND PROPERTIES OF ISOMERIC HYDROCARBON RADICAL SPECIES, C4H3

The molecular structures. relative stabilities and vibrational frequen cies of some selective hydrocarbon radical isomers of the C4H3 species obtained at the UMP/6-31G* level of theory are reported. Furthermore , the relative energies were estimated up to the PUMP4/6-31G* level o f accuracy by eliminating the spin contaminations. The present ab init io results are compared with those of previously reported semiempirica l MNDO or empirical MMP2 calculations, it is shown that the calculated geometrical parameters and the relative energies deviate appreciably from each other.